Dementia involves the progressive or fixed loss of cognitive functions in a person without previous deficiencies. In other words, a patient with dementia has lost cognitive capabilities that were previously present.
Dementia is a syndrome (rather than a specific disease) which may be caused by a broad array of pathologies. The cognitive loss associated with dementia goes beyond the mild to moderate degree of memory loss and cognitive slowing that is expected with normal aging.
Although the most common dementias are currently irreversible (including Alzheimer’s disease), there are multiple causes of dementia that are potentially reversible. These causes should be ruled out before assigning an Alzheimer’s disease diagnosis.
How do you diagnose dementia?
There are five steps to follow in the diagnosis of dementia:
- Obtain a good history
- Consider cardiovascular disease among your differentials
- Perform a full neurological exam and assess cognitive performance
- Order laboratory and diagnostic imaging tests
- Refer your patient to a neuropsychologist and neurologist
Step 1: Obtain a good history
When evaluating a patient for dementia, start with a good history. There are eight important details that will help you determine the cause of your patient’s dementia symptoms:
- Family history of Alzheimer’s disease
- History of significant head injury
- History of alcoholism or poor nutrition
- Presence of generalized fatigue
- Symptoms of depression
- Presence of gait disturbances or urinary incontinence
- Presence of hemiparesis or aphasia
- History of high-risk behaviors
Is there a family history of Alzheimer’s disease?
When obtaining a history from a patient with dementia, first determine if there is a strong family history of Alzheimer’s disease. Family history is not uncommon in Alzheimer’s disease, but it does not assure a diagnosis.
Has the patient sustained a significant head injury in the past?
A previous head injury may have led to static cognitive deficiencies, chronic subdural hematomas, or hydrocephalus. In other words, the patient may have lost cognitive function due to a substantial head injury.
Cognitive deficits are frequently seen in patients with severe closed head injuries. There may be a period of improvement that tends to flatten out over several months before whatever cognitive loss that has been sustained becomes permanent. This cognitive loss is not reversible; if the loss is substantial, it appears as dementia.
Previous trauma may also result in the accumulation of chronic collections of liquified subdural blood. These collections often increase in size over weeks to months and can appear as rapidly progressive dementia. With evacuation of the blood, the cognitive deficits can be totally reversible.
Similarly, even mild trauma can cause changes in cerebrospinal fluid (CSF) dynamics that result in progressive hydrocephalus. These changes may appear as progressive dementia over weeks or months and can be totally reversible with appropriate treatment. In this case, the appropriate treatment involves diversion (e.g., shunting) of the CSF out of the ventricular system.
Is there a history of alcoholism or poor nutrition?
A history of alcoholism or poor nutrition might point towards vitamin deficiencies or Wernicke's encephalopathy as the cause of the patient’s dementia symptoms.
Does the patient complain of generalized fatigue?
If the patient complains of generalized fatigue, in addition to dementia-like symptoms, be sure to rule out hypothyroidism.
Does the patient suffer from depression?
Remember that profound depression can mask as dementia. In other words, patients with severe depression often initially feel as though they are suffering from dementia.
On the other hand, patients with progressive dementia often initially feel as though they are simply depressed. Both disorders involve profound psychomotor retardation, diminished processing, diminished interest in their environments, changes in behavior, and errors in cognition.
Does the patient exhibit gait disturbances or urinary incontinence?
If the patient complains of urinary incontinence and shows evidence of gait disturbances, be sure to investigate for normal pressure hydrocephalus (NPH). It is not a particularly well-understood condition, but involves progressive ventricular dilation with no increased intracranial pressure.
Normal pressure hydrocephalus manifests as a progressive loss in cognitive processing and memory, often accompanied by urinary incontinence and magnetic gait (slowed gait with feet that appear to be sticking to the ground). A definitive diagnosis for NPH is difficult. Cerebral spinal fluid diversion from the ventricles results in symptom improvements (sometimes dramatically) for 50–70% of well-selected candidates.
Are focal neurological deficits such as hemiparesis or aphasia present?
Focal neurological deficits, such as hemiparesis or aphasia, may suggest an expanding cerebral mass. Tumors in the frontal lobes or tumors that result in increased intracranial pressure are initially mistaken by family members as dementia—particularly in elderly relatives. Sometimes, especially with benign tumors, cognitive dysfunction can be dramatically reversed by the removal of the tumor.
Does the patient have a history of engaging in high-risk behaviors?
If the patient admits to engaging in high-risk behavior, either presently or in the past, be sure to rule out human immunodeficiency virus (HIV) and syphilis.
Step 2: Consider cardiovascular disease among your differentials
Cerebrovascular disease resulting in multiple small cerebral infarcts can cause progressive cognitive dysfunctions. Cerebrovascular disease is not reversible, but mitigating vascular disease risk factors can help prevent its progression.
Step 3: Perform a full neurological exam and assess cognitive performance
Perform a full neurological exam to look for findings beyond cognitive loss, with a focus on cognitive performance. The Mini-Mental State Exam (MMSE) is a particularly powerful cognitive test that can be found online.
Multiple versions of cognitive evaluation tests are available online, all with their own nuances and interpretations. None of these evaluations are definitive, but low performance suggests a dementing process if other conditions have been ruled out.
Step 4: Order laboratory and diagnostic imaging tests
Order blood tests such as a complete blood count (CBC), metabolic panel, liver function tests, vitamin B12 levels, and thyroid function tests to rule out metabolic causes.
As well, order magnetic resonance imaging (MRI) for the brain to rule out structural causes of dementia, such as tumors, chronic subdural hematoma, NPH, or infarcts. Volumetric assessment of various anatomic brain structures (such as the hippocampus) is not currently considered to be of diagnostic value for dementia. Computed tomography (CT) scans of the brain can be acquired if the patient cannot undergo an MRI, but these are less sensitive to various pathologies.
Although employed in some centers, positron emission tomography (PET) scanning, CSF biomarker analysis, genotyping, and encephalography are not routinely recommended for the work-up of dementia.
Step 5: Refer your patient to a neuropsychologist and neurologist
Neuropsychometric testing with a neuropsychologist will often help to establish the type, degree, and progression rate of cognitive loss in your patient. If you suspect that a patient has non-reversible progressive dementia, an evaluation by a neurologist should be obtained.
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